Some vehicles have a roof rack for carrying cargos such as luggage or a bicycle. A conventional roof rack includes two parallel longitudinal rails fixed on a roof panel of the vehicle. A cargo can be secured to the rails via a rope or other fixing tools. DE patent application No. DE10200753A1 discloses a roof rack, including two longitudinal rails and at least two lateral beams. Each lateral beam is received in a longitudinal recess in the corresponding longitudinal rails at a stowed position, and rotated out from the longitudinal rails at a deployed position such that the longitudinal rails and lateral beams form a supporting structure to hold a large cargo like a skateboard, a bicycle, or a luggage case. The inventors of the present disclosure have recognized that the roof rack can provide other functions in addition to carry a cargo.